I began winter biking this year and found that riding at decent speeds in cold weather causes discomfort and my sinuses to dry out - resulting in sinusitis and sore throat. Wrapping a scarf over my face sorta worked, but I wanted a better solution. After some forum searches and googling, I decided to get the BreathXChange shield for about US$30.
The shield is a fairly simple affair with a fabric mask that contains a QXTEC heat exchanger, which looks somewhat like a mini car air-filter. The heat exchanger unit can be removed quite easily and the fabric mask and heat exchanger can be washed separately; the former can be thrown in a washing machine and the latter can be washed by hand. Wash instructions on the mask indicate that the whole unit can be machine washed, but I would be nervous putting the fragile-looking QXTEC module through a wash cycle. The mask is "one size fits most", and was a slightly tight fit on my XL face . I wore it on my ride in to work this AM. I was happy to find that the unit works as well as advertised. The heat from the exhaled breath is retained in the heat exchanger module and warms up the incoming air. I found that I was breathing in air that was at a temperature close to that of air on a warm spring/fall day. Considering that the ambient temperature was around 15F, this was a big improvement. Breathing through the exchanger adds some flow resistance, i.e., it makes breathing a little bit harder, but I did not find that it was a big problem. The heat exchanger module also retains some moisture according to the manufacturer's claim; this seems to work since the inhaled air seemed was not dry. One drawback was that, if I pulled up the mask to cover my nose, my sunglasses fogged up post haste. To avoid this, I let the top of the mask lie below my nose. This helped keep my sunglasses free of condensation. An additional point to note is that using the exchanger means that you will be breathing through your mouth exclusively rather than your nose. It was not a big problem for me, but YMMV. At the end of the ride, I was feeling quite good with no scratchy throat or dried out sinus issues.
Overall, I am very happy with the BreathXChange shield and would highly recommend it for anyone who has discomfort due to breathing in very cold air during the winter season (note: I am not affiliated with the manufacturer and vendor in any way).